With the advancement of optical telecommunication technologies optical components become increasingly complex and sophisticated in design. In an optical crossbar switch, also known as an optical cross connect (OXC), a multitude of optical communication lines may be simultaneously switched. The switching is typically performed by spatially directing focused signal beams between optical fiber interfaces. The focusing of a signal beam is commonly accomplished by placing a lens in front of the fiber end. This means that in a fiber interface with two dimensionally arrayed fiber ends lenses are arrayed in axial alignment with each fiber end.
Fiber interfaces are fabricated with ever increasing numbers of fibers while reducing the pitch between individual fiber axes. As a consequence, the fabrication of Lens arrays becomes increasingly challenging and cost intensive. To circumvent this problem, a modified OXC may be configured with a telecentric lens that simultaneously focuses a number of signal beams propagating towards and away from the fiber ends. In that context it is referred to the cross-referenced application for “Optical cross connect with simultaneous focusing of discrete signal beams”.
A core component of such a modified OXC is a multi-surface optical component that is placed after the telecentric lens. The multi-surface component has a number of individually positioned optical surfaces configured and positioned such that each of the simultaneously focused signal beams impinges on a predetermined optical surface and is directed onto a moveable mirror element within a mirror array where the signal beams are spatially redirected for switching purposes.
In the preferred embodiment, the optical surfaces are planar mirrors that direct the signal beams onto individual mirrors within the moveable mirror array by means of reflection. The efficiency and dimensional scale of the modified OXC is highly dependent on the position and orientation precision with which the individual mirrors are positioned and oriented on the multi-surface component.
Optical components with multiple optical surfaces have been fabricated in several ways. In the case where a relatively low number of optical surfaces are combined and spatially arrayed with an angle between adjacent optical surfaces of more than 180 degrees, the fabrication is relatively easily accomplished. For example, U.S. Pat. No. 5,692,287 to Nakamura et al teaches a method for making a polygon mirror by machining the mirror surfaces from a monolithic metal block. As can be seen in the Figures, the fabrication of the mirror surfaces is relatively simple since the machining tool may extend beyond the individual mirror's boundaries without interfering with other mirror surfaces. Also the number and arrangement of the individual mirror surfaces does not impose unusual effort in the setup process of the work piece on the fabrication machine.
In cases where a high number of small optical surfaces needs to be fabricated with high precision into a single optical component, machining of the individual optical surfaces becomes arduous. For each optical surface, the monolithic block would need to be positioned accurately with respect to the machining tools machining plane. In cases where the optical surfaces are spatially positioned relative to each other, accurate machining positioning is difficult to accomplish. Secondly, the machining of a high number of independent optical surfaces into a single work piece bears an increasing risk of machining errors that grows with the number of optical surfaces.
In cases where the angle between adjacent optical surfaces is less than 180 degrees, machining becomes much more complicated, since the machining tool may not extend beyond the intersections of adjacent optical surfaces. Hence, machining is typically a highly unfeasible fabrication method for optical components with concavely arrayed optical surfaces.
In a modified OXC, the multi-surface component has to provide a number of discrete optical surfaces that is at least as high as the number of switched lines. As the switching capacity of an OXC advances to simultaneous switching of several thousand signal beams, there arises a need for new ways of efficiently fabricating a multi-surface component.
In one approach, individual optical elements are prefabricated with a single discrete optical surface. The optical elements are then assembled together in a one by one fashion. This is accomplished by spatially positioning each optical element in a fixture while bonding them to one another or to a support structure. The fixture provides the accurate positioning of the optical element while the bonding takes place. The spatial fixing of the optical elements requires the separate adjustment of six degrees of freedom (Translations in X,Y,Z and Tip, Tilt, and Clocking) for each individual mirror element. Even though this method may have some use in cases where a low number of optical elements are combined in a single optical component, the method is highly unpractical for fabricating optical components having a large number of discrete optical surfaces.
Therefore, there exists a need for an efficient and precise fabrication method for optical components having a large number of optical surfaces. The invention described in the following addresses this need.